The proposed experiments are addressed to the question, "How do specific sites on the genome interact with those proteins which are involved in mediating and regulating the expression of the genome?" The three regions which are being studied are the promoters of bacteriophage lambda, the regulatory sequences of the lac operon, and the promoters of the tyrosine tRNA genes. Site-specific endodeoxyribonucleases are used to obtain specific DNA fragments which are fractionated by polyacrylamide-agarose gel electrophoresis. The desired fragments are identified by their ability to interact with the appropriate protein or RNA molecules and/or by their location in a reconstructed "genetic" map of the individual fragments. The desired fragments will be isolated in preparative quantities and the nucleotides sequence of the relevant regions determined. By a comparison of different but analogous regions, by the sequencing of selected mutants, and by in vitro biochemical analysis of the isolated fragments, attempts will be made to correlate the structure of these genomic regions with their known biological properties. It is also proposed to continue present experiments on the enzymology of site-specific deoxyribonucleases, procedures for fractionating specific DNA fragments, and the application of these techniques to eucaryote DNAs.